I lay the cd or dvd on a piece of newpaper, put a nickel over the hole, and spray it. The only problems I've had were from not having a flat enough surface. They spray would work its way under the edge of the disc.
The glossy stuff seems to leave imperfections....a little bubble or mark here or there...maybe it's thicker going on or something...
krylon makes several other clear coat type sprays, perhaps another type would go on more reliably.
The matte coat works well, and makes the inkjet printed disc smudge/water resistant.